Preparation of trimethylsilyl group containing copolymer for negative-type photoresists that enable stripped by an alkaline solution

A series of four trimethylsilyl group containing copolymers were synthesized using the solution free-radical co-polymerization with azobisisobutyronitrile (AIBN) in 1,4-dioxane at 60degreesC. The photoresists were prepared by dissolving copolymer, one of two kind photosensitizer (dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate) and Michler's ketone in tetrahydrofuran (THF). The cyclic maleimide group was responsible for the high thermal stabilities. After irradiation by a deep-ultraviolet light and development with mixed solvent (methyl isobutyl ketone: 2-propanol = 1:3), the developed patterns showed negative images and exhibited good adhesion to the silicon wafer without using any adhesion promoter. The resolution of the resists was at least 1.75 mum and the oxygen plasma etching rate was 1/6 of hard-baked HPR-204, which can be also used as the top-imaging layer of a bilayer resist for micro-lithographic application. These photoresists can be stripped by week alkaline solution such as sodium carbonate solution (0.01 wt%) after exposure. (C) 2002 Elsevier Science Ltd. All rights reserved.